Prior to this change, the schematic connectivity was updated any time a
change was made to a connectable object.  Now the connectivity is only
updated when an object change actually affects the connectivity.  Other
properties like line width, fill type, custom fonts, etc. will not cause
the connectivity graph to be rebuilt.

The SCH_COMMIT flag SKIP_CONNECTIVITY has been removed.  All schematic
objects can test if they are connectable and if there have been changes
to any connection properties that require a connectivity rebuild.

Remove duplicate rebuild connectivity calls from editor control tool.
This was causing the tangling end test to get called four times on every
undo and redo action because the dangling end test is already called in
the connectivity graph calculation code.

Update connectivity when changing label names which fixes an unreported
connectivity bug.

(cherry picked from commit c5a02fc2)